Light-emitting diodes (LEDs) may be assembled in high-efficiency and high-brightness lighting applications. The brightness of LEDs may directly relate to forward current flowing through the LEDs. In general, the LEDs become brighter as the forward current increases. Usually, the forward current should be precisely balanced in order to obtain brightness balancing between a plurality of LEDs. Typically, an LLC resonant DC/DC converter is used in LED drivers because of its high conversion efficiency. As shown in FIG. 1, an example LLC resonant DC/DC converter can include two rectifier loops connected with the secondary winding. This approach can achieve current balancing without any active component or active controlling methods, but only through blocking capacitor C1.
However, a converter of this kind can only achieve current balancing between two LED strings. When a plurality of LEDs are connected in series to form an LED string, the cross voltage on each LED strings may be too high and result in an increase of a withstand voltage of the LED string. Also, forward voltage drops on diodes with high withstand voltages can be substantially large, so conduction losses and reverse recovery losses cannot be ignored. Therefore, it may become difficult to improve system conversion efficiency, and design and production costs may be increased due to relatively large bulk capacitors configured as filter capacitors.